Simultaneous serotonin and dopamine monitoring across timescales by rapid pulse voltammetry with partial least squares regression.

Many voltammetry methods have been developed to monitor brain extracellular dopamine levels. Fewer approaches have been successful in detecting serotonin in vivo. No voltammetric techniques are currently available to monitor both neurotransmitters simultaneously across timescales, even though they play integrated roles in modulating behavior. We provide proof-of-concept for rapid pulse voltammetry coupled with partial least squares regression (RPV-PLSR), an approach adapted from multi-electrode systems (i.e., electronic tongues) used to identify multiple components in complex environments. We exploited small differences in analyte redox profiles to select pulse steps for RPV waveforms. Using an intentionally designed pulse strategy combined with custom instrumentation and analysis software, we monitored basal and stimulated levels of dopamine and serotonin. In addition to faradaic currents, capacitive currents were important factors in analyte identification arguing against background subtraction. Compared to fast-scan cyclic voltammetry-principal components regression (FSCV-PCR), RPV-PLSR better differentiated and quantified basal and stimulated dopamine and serotonin associated with striatal recording electrode position, optical stimulation frequency, and serotonin reuptake inhibition. The RPV-PLSR approach can be generalized to other electrochemically active neurotransmitters and provides a feedback pipeline for future optimization of multi-analyte, fit-for-purpose waveforms and machine learning approaches to data analysis.

Performance characteristics of five SARS-CoV-2 serological assays: Clinical utility in health-care workers.

STUDY OBJECTIVE: SARS-CoV-2, which causes coronavirus disease (COVID-19), continues to cause significant morbidity and mortality. The diagnosis of acute infection relies on reverse transcription-polymerase chain reaction (RT-PCR)-based viral detection. The objective of this study was to evaluate the optimal serological testing strategy for anti-SARS-CoV-2 antibodies which provides an important indicator of prior infection and potential short-term immunity. METHODS: The sensitivity and specificity of four different ELISA assays (Euroimmun IgG, Euroimmun NCP-IgG, Fortress and DIAsource) and one CLIA assay (Roche ELECSYS) were evaluated in 423 samples; 137 patients with confirmed RT-PCR COVID-19 infection (true positives), and 100 pre-pandemic samples collected prior to October 2019 (true negatives). A further 186 samples were collected from health-care staff and analysed by all five assays. RESULTS: The Fortress ELISA assay demonstrated the highest sensitivity and specificity followed by the Roche ECLIA assay. The highest overall sensitivity came from the assays that measured total antibody (IgM-IgG combined) and the three assays that performed the best (Fortress, Roche, Euroimmun IgG) all have different antigens as their target proteins which suggests that antigen target does not affect assay performance. In mildly symptomatic participants with either a negative RT-PCR or no RT-PCR performed, 16.76% had detectable antibodies suggesting previous infection. CONCLUSIONS: We recommend a combined testing strategy utilizing assays with different antigenic targets using the fully automated Roche ECLIA assay and confirming discordant samples with the Fortress Total Antibody ELISA assay. This study provides an important indicator of prior infection in symptomatic and asymptomatic individuals.

Entropy-driven electrochemiluminescence ultra-sensitive detection strategy of NF-κB p50 as the regulator of cytokine storm.

2019 novel coronavirus (2019-nCoV) with strong contagion in the crowd, has ravaged worldwide and severely impacts the human health and epidemic prevention system, by producing a series of significant stress reactions in the body to induce further cytokine storm. Transcription factors (TFs) served as essential DNA binding proteins play an integral role in regulating cytokine storm, and the detection of it in the human coronavirus environment provides especially valuable approaches to diagnosis and treatment of 2019-nCoV and development of antiviral drugs. In this work, an entropy-driven electrochemiluminescence (ECL) biosensor was constructed for ultra-sensitive bioassay of NF-κB p50. The strategy primarily capitalizing the splendid double-stranded DNA (dsDNA) binding properties of transcription factors, employing GOAu-Ru composite material as ECL emitter, utilizing entropy-driven reactions for signal amplification method, offered a repeatable proposal for TFs detection. In the absence of TFs, the released DNA1 further went in the entropy-driven reaction, contributing to an "ECL off" state. However, in the presence of TFs, the dsDNA avoided being digested, which blocked DNA1 for participating in the entropy-driven reaction, and the system exhibited an "ECL on" state. Most importantly, the ECL bioanalytical method denoted broad application prospects for NF-κB p50 detection with a lower detection limit (9.1 pM).

Highly precise characterization of the hydration state upon thermal denaturation of human serum albumin using a 65 GHz dielectric sensor.

The biological functions of proteins depend on harmonization with hydration water surrounding them. Indeed, the dynamical transition of proteins, such as thermal denaturation, is dependent on the changes in the mobility of hydration water. However, the role of hydration water during dynamical transition is yet to be fully understood due to technical limitations in precisely characterizing the amount of hydration water. A state-of-the-art CMOS dielectric sensor consisting of 65 GHz LC resonators addressed this issue by utilizing the feature that oscillation frequency sensitively shifts in response to the complex dielectric constant at 65 GHz with extremely high precision. This study aimed to establish an analytical algorithm to derive the hydration number from the measured frequency shift and to demonstrate the transition of hydration number upon the thermal denaturation of human serum albumin. The determined hydration number in the native state drew a "global" hydration picture beyond the first solvation shell, with substantially reduced uncertainty of the hydration number (about ±1%). This allowed the detection of a rapid increase in the hydration number at about 55 °C during the heating process, which was in excellent phase with the irreversible rupture of the α-helical structure into solvent-exposed extended chains, whereas the hydration number did not trace the forward path in the subsequent cooling process. Our result indicates that the weakening of water hydrogen bonds trigger the unfolding of the protein structure first, followed by the changes in the number of hydration water as a consequence of thermal denaturation.

Voltammetric analysis for distinguishing portal hypertension-related from malignancy-related ascites: A proof of concept study.

BACKGROUND: Serum-ascites albumin gradient (SAAG) remains the most sensitive and specific marker for the differentiation of ascites due to portal hypertension from ascites due to other causes. SAAG has some limitations and may fail in selected conditions. Voltammetric analysis (VA) has been used for the detection of electroactive species of biological significance and has proven effective for detection infections in biological fluids. AIMS: In this study, we compared the accuracy of voltammetric analysis (VA) with that of SAAG to differentiate ascites due to portal hypertension from that having a different origin. METHODS: 80 ascites samples were obtained from patients undergoing paracentesis at the Campus Bio-Medico Hospital of Rome. VA was performed using the BIONOTE device. The ability of VA to discriminate ascitic fluid etiology and biochemical parameters was evaluated using Partial Least Square Discriminant Analysis (PLS-DA), with ten-fold cross-validations. RESULTS: Mean age was 68.6 years (SD 12.5), 58% were male. Ascites was secondary to only portal hypertension in 72.5% of cases (58 subjects) and it was secondary to a baseline neoplastic disease in 27.5% of cases (22 subjects). Compared to SAAG≥1.1, e-tongue predicted ascites from portal hypertension with a better accuracy (92.5% Vs 87.5%); sensitivity (98.3% Vs 94.8%); specificity (77.3% Vs 68.2%); predictive values (PPV 91.9% Vs 88.7% and NPV 94.4% Vs 83.3%). VA correctly classified ascites etiology in 57/58 (98.2%) of cases with portal hypertension and in 17/22 (77.2%) of cases with malignancy. Instead, VA showed poor predictive capacities towards total white blood count and polymorphonuclear cell count. CONCLUSIONS: According to this proof of concept study, VA qualifies as a promising low-cost and easy method to discriminate between ascites secondary to portal hypertension and ascites due to malignancy.

Application of chemometrics for detection and modeling of adulteration of fresh cow milk with reconstituted skim milk powder using voltammetric fingerpriting on a graphite/ SiO2 hybrid electrode.

In the present work, an analytical approach for the voltammetric detection and prediction of adulteration of fresh cow milk with reconstituted skim milk powder is developed. After precipitation of milk proteins upon addition of ethanol and centrifugation, the supernatant liquid of the samples was analyzed by cyclic voltammetry on a novel graphite/SiO2 hybrid working electrode (GSiHE) using LiClO4 as electrolyte. Under these conditions, fresh milk samples gave broadened peaks/plateaus in both forward and backward potential scanning, attributed mainly to oxidases. Such peaks were not evident in the case of reconstituted skim milk powder samples due to inactivation of enzymes and breakdown of certain antioxidants caused by heat and pressure-treatments. The differences between fresh and reconstituted skim milk powder samples in their voltammetric profile were exploited for the detection of fresh milk adulteration by submitting voltammetric data to chemometrics. As datapoints, the differences between forward and backward current values, recorded at the same potentials, were determined and submitted to multivariate analysis. Principal Component Analysis (PCA) provided a clear differentiation between fresh milk and reconstituted skim milk powder samples. Soft independent modeling of class analogy (SIMCA) was employed to model the class of fresh milks, using samples from 12 commercially available fresh milk brands. Prediction of fresh milk adulteration with reconstituted skim milk powders was achieved by means of Partial Least Squares (PLS) regression analysis. Detection limit of the technique was found to be below 6% (v/v) and the linearity of model in terms of observed/predicted values was confirmed up to 100% (v/v). Validation and applicability of both SIMCA and PLS models were confirmed using a suitable test set, consisting of commercial fresh milk and skim milk powder samples as well as synthetic adulterated fresh milk samples.

Standard addition method with cumulative additions: Monte Carlo uncertainty evaluation.

The cumulative standard addition method allows the calibration of an instrument affected by matrix effects when a small sample volume is available. Recently, it was developed and validated a metrologically sound procedure to estimate the uncertainty of these measurements based on the modelling of the uncertainty of the extrapolation of the calibration curve by the linear least squares regression model. However, this procedure is only applicable when the uncertainty of cumulative sample dilutions and analyte mass additions are negligible given the uncertainty of the total solution volume (v) times the instrumental signal (I) (i.e. v∙I). This work developed a measurement uncertainty model, not limited by this assumption of the quality of calibrators preparation, based on Monte Carlo simulations. This method was successfully applied to the voltammetric measurements of uric acid in human serum, using a working nanocarbon electrode modified with Cu-nanocarbon-lignin, since the uncertainty model adapts to the uncertainty of cumulative volume additions. The validated procedure was checked through the analysis of spiked physiological serum samples and human serum samples, by assessing the metrological compatibility between estimated and reference values. The measurements are reported with an expanded uncertainty not larger than a target value of 0.56 mg dL-1. The used spreadsheet is made available as supplementary material.

Carbon nanotube-based aptasensor for sensitive electrochemical detection of whole-cell Salmonella.

In this study, an amino-modified aptasensor using multi-walled carbon nanotubes (MWCNTs)-deposited ITO electrode was prepared and evaluated for the detection of pathogenic Salmonella bacteria. An amino-modified aptamer (ssDNA) which binds selectively to whole-cell Salmonella was immobilised on the COOH-rich MWCNTs to produce the ssDNA/MWCNT/ITO electrode. The morphology of the MWCNT before and after interaction with the aptamers were observed using scanning electron microscopy (SEM). Cyclic voltammetry and electrochemical impedance spectroscopy techniques were used to investigate the electrochemical properties and conductivity of the aptasensor. The results showed that the impedance measured at the ssDNA/MWCNT/ITO electrode surface increased after exposure to Salmonella cells, which indicated successful binding of Salmonella on the aptamer-functionalised surface. The developed ssDNA/MWCNT/ITO aptasensor was stable and maintained linearity when the scan rate was increased from 10 mV s-1 to 90 mV s-1. The detection limit of the ssDNA/MWCNT/ITO aptasensor, determined from the sensitivity analysis, was found to be 5.5 × 101 cfu mL-1 and 6.7 × 101 cfu mL-1 for S. Enteritidis and S. Typhimurium, respectively. The specificity test demonstrated that Salmonella bound specifically to the ssDNA/MWCNT/ITO aptasensor surface, when compared with non-Salmonella spp. The prepared aptasensor was successfully applied for the detection of Salmonella in food samples.

An impedimetric immunosensor for highly sensitive detection of IL-8 in human serum and saliva samples: A new surface modification method by 6-phosphonohexanoic acid for biosensing applications.

In this study, we fabricated a sensitive and label-free impedimetric immunosensor based on 6-phosphonohexanoic acid (PHA) modified ITO electrode for detection of interleukin-8 (IL-8) in human serum and saliva. PHA was first employed to cancer biomarker sensing platform. Anti-IL-8 antibody was used as a biorecognition element and the detection principle of this immunosensor was based on monitoring specific interaction between anti-IL-8 antibody and IL-8 antigen. The morphological characterization of each electrode modification step was analyzed by scanning electron microscopy (SEM), SEM-energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM) while electrochemical characterization was performed by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and single frequency impedance (SFI) techniques. Moreover, the antibody immobilization on the electrode surface was proved Fourier-transform infrared spectroscopy (FTIR) and Raman Spectroscopy. This proposed impedimetric immunosensor exhibited good performances with a wide linear in the range from 0.02 pg/mL to 3 pg/mL as well as a relative low detection limit of 6 fg/mL. The impedimetric immunosensor had a good specificity, stability and reproducibility. This study proved that PHA was a suitable interface material to fabricate an electrochemical biosensor.

Highly sensitive electrochemical detection of genomic DNA based on stem loop probes structured for magnetic collection and measurement via metalised hollow polyelectrolyte shells.

We report a highly sensitive method for the electrochemical detection of genomic DNA, based on the employment of two sub-micron oligonucleotide labels - one for magnetic collection and the other for voltammetric detection - and their incorporation onto a stem loop DNA probe. The magnetic label consists of a latex particle of mean diameter 441±6 nm, bearing magnetic Fe3O4 particles and approx. 3.5×10(5) anti-DIG antibodies. The voltammetric label is a hollow polyelectrolyte shell containing approx. 1.0×10(11) Au atoms in the form of well dispersed Au nanoparticles. A DIG tag on one arm of the stem loop enables binding to the magnetic label, while a thiol tag on the other arm enables attachment to the Au nanoparticles. Due to steric hindrance from the two relatively large labels, attachment of both moieties is dependant on target-probe hybridisation straightening the loop. Once attached, sensitive DNA measurement is facilitated by magnetic collection of the DNA into a small volume and by the high quantity of Au atoms available for detection. Using differential pulse anodic stripping voltammetry we calibrated a 30 mer sequence common to 71 strains of Escherichia coli across the concentration range from 0.1 aM to 100 pM with a LOD of 1.8 aM. Three strains of E. coli, BL 21, ATCC8739, O157:H7, when spiked into UHT milk and fermented palm juice, could be detected with LODs of approx. 2-4 CFU mL(-1) in an assay time of approx. 140 min.

Selective determination of isoniazid using bentonite clay modified electrodes.

Fe(dmbpy)3(2+) (where dmbpy is 4,4'-dimethyl-2,2'-bipyridine) was immobilized by ion-exchange in a bentonite clay film coating on a glassy carbon electrode. Cyclic voltammetry characteristics of the immobilized Fe(dmbpy)3(2+) were stable and reproducible corresponding to the Fe(dmbpy)3(2+/3+) redox process. In the presence of isoniazid (IZ), the electrogenerated in film Fe(dmbpy)3(3+) oxidized IZ efficiently producing large anodic current. This current was linearly proportional to the IZ concentration in the solution. The process was described by an EC' electrocatalysis mechanism allowing for sensitive determination of IZ with a wide linear dynamic concentration range of 10.0µM to 10.0mM. The electrode was tested for its analytical suitability and possible discrimination of interferences by determining IZ in a commercially available pharmaceutical product. The paper reports on a simple, cheap, and easy to fabricate chronoamperometric chemical sensor for determination of IZ. Kinetic parameters, such as the catalytic rate constant (2.3×10(3)M(-1)s(-1)) and diffusion coefficient of IZ (5.42×10(-5)cm(2)s(-1)), were determined using CV, chronoamperometry, and chronocoulometry.

An electrochemical sensor for selective TNT sensing based on Tobacco mosaic virus-like particle binding agents.

This paper presents a selective differential sensing method based on diffusion modulation of the target molecules through suspended Tobacco mosaic virus-like particles modified with binding peptides for TNT sensing in solution.

Tantalum electrodes modified with well-aligned carbon nanotube-Au nanoparticles: application to the highly sensitive electrochemical determination of cefazolin.

Carbon nanotube/nanoparticle hybrid materials have been proven to exhibit high electrocatalytic activity suggesting broad potential applications in the field of electroanalysis. For the first time, modification of Ta electrode with aligned multi-walled carbon nanotubes/Au nanoparticles introduced for the sensitive determination of the antibiotic drug, cefazolin (CFZ). The electrochemical response characteristics of the modified electrode toward CFZ were investigated by means of cyclic and linear sweep voltammetry. The modified electrode showed an efficient catalytic activity for the reduction of CFZ, leading to a remarkable decrease in reduction overpotential and a significant increase of peak current. Under optimum conditions, the highly sensitive modified electrode showed a wide linear range from 50 pM to 50 µM with a sufficiently low detection limit of 1 ± 0.01 pM (S/N = 3). The results indicated that the prepared electrode presents suitable characteristics in terms of sensitivity (458.2 ± 2.6 µAcm(-2)/µM), accuracy, repeatability (RSD of 1.8 %), reproducibility (RSD of 2.9 %), stability (14 days), and good catalytic activity in physiological conditions. The method was successfully applied for accurate determination of trace amounts of CFZ in pharmaceutical and clinical preparations without the necessity for samples pretreatment or any time-consuming extraction or evaporation steps prior to the analysis.

A review on the electrochemical biosensors for determination of microRNAs.

MicroRNAs (miRNAs) are a family of non-protein-coding, endogenous, small RNAs. They are a group of gene regulators that function mainly by binding the 3' untranslated regions of specific target messenger RNA (mRNA) leading to gene inactivation by repression of mRNA transcription or induction of mRNA. Mature miRNAs are short molecules approximately 22 nucleotides in length. They regulate a wide range of biological functions from cell proliferation and death to cancer progression. Cellular miRNA expression levels can be used as biomarkers for the onset of disease states and in gene therapy for genetic disorders. Methods for detection of miRNA mainly include northern blotting, microarray, polymerase chain reaction (PCR). This review focuses on the use of electrochemical biosensors for the detection of microRNA.

Glyphosate detection with ammonium nitrate and humic acids as potential interfering substances by pulsed voltammetry technique.

Pulsed voltammetry has been used to detect and quantify glyphosate on buffered water in presence of ammonium nitrate and humic substances. Glyphosate is the most widely used herbicide active ingredient in the world. It is a non-selective broad spectrum herbicide but some of its health and environmental effects are still being discussed. Nowadays, glyphosate pollution in water is being monitored but quantification techniques are slow and expensive. Glyphosate wastes are often detected in countryside water bodies where organic substances and fertilizers (commonly based on ammonium nitrate) may also be present. Glyphosate also forms complexes with humic acids so these compounds have also been taken into consideration. The objective of this research is to study the interference of these common pollutants in glyphosate measurements by pulsed voltammetry. The statistical treatment of the voltammetric data obtained lets us discriminate glyphosate from the other studied compounds and a mathematical model has been built to quantify glyphosate concentrations in a buffer despite the presence of humic substances and ammonium nitrate. In this model, the coefficient of determination (R(2)) is 0.977 and the RMSEP value is 2.96 × 10(-5) so the model is considered statistically valid.

Sensitive electrochemical immunosensor for α-synuclein based on dual signal amplification using PAMAM dendrimer-encapsulated Au and enhanced gold nanoparticle labels.

A novel electrochemical immunosensor for sensitive detection of α-synuclein (α-SYN), a very important neuronal protein, has been developed based on dual signal amplification strategy. Herein, G4-polyamidoamine dendrimer-encapsulated Au nanoparticles (PAMAM-Au nanocomposites) were covalently bound on the poly-o-aminobenzoic acid (poly-o-ABA), which was initially electropolymerized on the electrode surface to perform abundant carboxyl groups. The formed immunosensor platform, PAMAM-Au, was proved to provide numerous amino groups to allow highly dense immobilization of antigen, and facilitate the improvement of electrochemical responses as well. Subsequently, the enhanced gold nanoparticle labels ({HRP-Ab(2)-GNPs}) were fabricated by immobilizing horseradish peroxidase-secondary antibody (HRP-Ab(2)) on the surface of gold nanoparticles (GNPs). After an immunoassay process, the {HRP-Ab(2)-GNPs} labels were introduced onto the electrode surface, and produced an electrocatalytic response by reduction of hydrogen peroxide (H(2)O(2)) in the presence of enzymatically oxidized thionine. On the basis of the dual signal amplification of PAMAM-Au and {HRP-Ab(2)-GNPs} labels, the designed immunosensor displayed an excellent analytical performance with high sensitivity and stability. This developed strategy was successfully proved as a simple, cost-effective method, and could be easily extended to other protein analysis schemes.

Multichannel bipotentiostat integrated with a microfluidic platform for electrochemical real-time monitoring of cell cultures.

An electrochemical detection system specifically designed for multi-parameter real-time monitoring of stem cell culturing/differentiation in a microfluidic system is presented. It is composed of a very compact 24-channel electronic board, compatible with arrays of microelectrodes and coupled to a microfluidic cell culture system. A versatile data acquisition software enables performing amperometry, cyclic voltammetry and impedance spectroscopy in each of the 12 independent chambers over a 100 kHz bandwidth with current resolution down to 5 pA for 100 ms measuring time. The design of the platform, its realization and experimental characterization are reported, with emphasis on the analysis of impact of input capacitance (i.e., microelectrode size) and microfluidic pump operation on current noise. Programmable sequences of successive injections of analytes (ferricyanide and dopamine) and rinsing buffer solution as well as the impedimetric continuous tracking for seven days of the proliferation of a colony of PC12 cells are successfully demonstrated.

A new way for synthesis of phenoxazine and diphenoxazine derivatives via electrochemical method.

Electrochemical oxidation of hydroquinone (1a) and 2,3-dimethylhydroquinone (1b) have been studied in the presence of 2-aminophenol (3a) and 2-amino-4-chlorophenol (3b), as nucleophiles in phosphate buffer solution (pH 7.2) using cyclic voltammetry and controlled potential coulometry. We proposed different mechanisms for the electrode process. The products were derived with good yield and purity using controlled-potential electrochemical oxidation of 1a, b in the presence of 3a and 3b at the graphite electrode in an undivided cell.

Comparison of four distinct detection platforms using multiple ligand binding assay formats.

Several detection platforms are available for ligand binding assays (LBA), each claiming superiority in sensitivity and dynamic range. However, little information exists in the literature directly comparing the various LBA platforms for quantitation. We have tested four common platforms to evaluate and compare the interchangeability of detection platforms by comparing sensitivity and dynamic range to a colorimetric LBA. The detection platforms compared are: colorimetric, chemiluminescence, time-resolved fluorescence (TRF) and electrochemiluminescence (ECL). Five different LBA protocols were tested with each of the detection endpoints. The assay protocols include the following ligand binding assay formats: direct binding, sandwich ELISA, competitive and cell based ELISA. We found that no detection platform consistently performed better than all the others and it was not possible to predict which platform would perform best for a given assay protocol. We also found surprising differences in assays (plate coating efficiency, low signal) which add to difficulty in choosing the best platform ad hoc. We propose here that in developing new assay protocols for detection of biotherapeutic agents, multiple detection platforms should be tested in order to forward the best assays possible and for the right reasons.

High-sensitivity electrochemical enzyme-linked assay on a microfluidic interdigitated microelectrode.

A novel enzyme-linked DNA hybridization assay on an interdigitated array (IDA) microelectrode integrated into a microfluidic channel is demonstrated with sub-nM detection limit. To improve the detection limit as compared to conventional electrochemical biosensors, a recyclable redox product, 4-aminophenol (PAP) is used with an IDA microelectrode. The IDA has a modest and easily fabricated inter-digit spacing of 10 µm, yet we were able to demonstrate 97% recycling efficiency of PAP due to the integration in a microfluidic channel. With a 70 nL sample volume, the characterized detection limit for PAP of 1.0 × 10⁻¹° M is achieved, with a linear dynamic range that extends from 1.0 × 10⁻9 to 1.0 × 10⁻5 M. This detection limit, which is the lowest reported detection limit for PAP, is due to the increased sensitivity provided by the sample confinement in the microfluidic channel, as well as the increased repeatability due to perfectly static flow in the microchannel and an additional anti-fouling step in the protocol. DNA sequence detection is achieved through a hybridization sandwich of an immobilized complementary probe, the target DNA sequence, and a second complementary probe labeled with ß-galactosidase (ß-GAL); the ß-GAL converts its substrate, 4-aminophenyl-d-galactopyranoside (PAPG), into PAP. In this report we present the lowest reported observed detection limit (1.0 × 10⁻¹° M) for an enzyme-linked DNA hybridization assay using an IDA microelectrode and a redox signaling paradigm. Thus, we have demonstrated highly sensitive detection of a targeted DNA sequence using a low-cost easily fabricated electrochemical biosensor integrated into a microfluidic channel.